Positive displacement apparatus of the scroll type have generated substantial interest for a number of reasons. For one, they are relatively simple. For another, their physical size may be relative small as compared to other types of positive displacement apparatus having the same capacity.
Their use, however, is not without attendant difficulties. As is well known, such apparatus constitutes two facing scroll plates each having spiral type vanes which interfit to define a plurality of closed pockets. When one of the scrolls is orbited relative to the other, the pockets travel between radially inner and outer ports to convey the working fluid.
Because there will always be a zone of high pressure at the interface between the scrolls during operation, such pressure tends to axially move the scrolls apart and such moving tends to interfere with proper sealing of the pockets both on the flanks and on the tips of the vanes. And, as sealing efficiency is lost, the efficiency of the apparatus likewise suffers.
To overcome this difficulty, the prior art has proposed that the scrolls be axially preloaded towards each other. The preload is sufficient to resist the separating force applied to the scrolls during the operation of the apparatus. However when the apparatus is quiescent, the preload results in relatively high frictional forces existing between the scrolls and/or bearings supporting the same. As a consequence, the initiation of operation of the apparatus becomes much more difficult.
To avoid this problem, the prior art has proposed the application of a pressurized fluid to one or both of the scrolls opposite the interface. Thus, a force resisting the separating force is generated and through known techniques, the two forces may be made to balance. U S. Pat. No. 4,384,831 issued May 24, 1983 to Ikegawa is representative of this approach. It will be observed that this approach is applied in the context of a scroll apparatus of the type wherein one scroll is stationary and the other is orbited with respect thereto. As is well known in the art, there is another common sort of scroll apparatus, namely, one wherein both scrolls rotate simultaneously while one of the scrolls is orbited with respect to the other at the same time. The approach applied by Ikegawa has not been applied to scroll apparatus of the latter type because of the problems of sealing a stationary chamber located opposite the interface of the scroll with a rotating or a rotating and orbiting scroll. In particular, though the seals would be curved, they would be moving across the relatively moving surface between the chamber and the scroll generally along their long dimension, much like an ice skate moving across ice. The skating action is subject to lubrication difficulties and accelerated wear with the result that the pressure balancing approach mentioned previously is not known to have been applied to scroll type apparatus of the type wherein both scrolls rotate with one scroll additionally orbiting with respect to the other.
The present invention is directed to overcoming this problem.